Hollow Cylinder Apparatus (GDS SS-HCA)

Transcription

1 HCA:1 Options available for SS-HCA Axial Load/Torque 1kN/1Nm 1kN/2Nm 12kN/2Nm 15kN/4Nm Dynamic upgrade frequencies Hollow Cylinder Apparatus (GDS SS-HCA).5Hz 2Hz 1Hz 5Hz Sample Height/Outer Ø/Inner Ø 2/1/6mm 4/2/16mm Custom Radial Stress (Cell Pressure) 2/1/6mm = 2MPa 4/2/16mm = 1MPa Additional Notes Complete Triaxial System What is it? The GDS Small-Strain Hollow Cylinder Apparatus (SS-HCA) allows for rotational displacement and torque to be applied to a hollow cylindrical specimen of soil. Using this device it is possible to control the magnitude and direction of the three principal stresses. Studies can for example be made of the following: The anisotropy of soil samples. The effects of principal stress rotation. The effects of intermediate principal stress. The SS-HCA has been designed to be a high quality, low cost hollow cylinder apparatus. It has specifically been designed to be capable of testing at very small axial strains (down to.4%). The GDS SS-HCA can apply a uniquely wide range of stress paths on the test specimen. The loading systems are computer controlled and strains can be measured directly on the test specimen. These strains can also be servo-controlled. Studies can therefore be made under the following test conditions: Plane strain. Simple shear. Very small shear strain. Two versions of the SS-HCA are available, a dynamic (SS- HCA d) and a lower cost "static" (SS-HCA s) version. The SS- HCA d has been developed to be a complete dynamic hollow cylinder apparatus (dynamic axial and rotational axes) at a price approaching that of a standard dynamic triaxial system. Technical specification Axial/Torque force range: 5kN/1Nm, 1kN/2Nm, 12kN/2Nm, 15kN/4Nm Specimen sizes (height /outer dia./inner dia.): 2/1/6mm or 4/2/16mm Transducer Resolution (based on 3kN/3Nm load cell). Dynamic values as a guide only as depend on machine spec. Axial Load: Dynamic SS-HCA d = <3N, Static SS-HCA s = <.7N Axial Displacement Encoder: Dynamic SS-HCA d = <1μm, Static SS-HCA s = <.8μm Torque: Dynamic SS-HCA d = <.3Nm, Static SS-HCA s = <.8Nm Rotational Encoder: Dynamic SS-HCA d = <.4 degrees, Static SS-HCA s = <.11 degrees Optional Local strain transducers: Hall effect 6mm range LVDT 5mm or 1mm range Non-contacting proximity transducers.9 to 6mm range. Optional transducers for measuring inner sample strain Optional large cell with i.d. of 5mm to provide additional space around sample for local instrumentation research 18 port built in transducer access ring Size:7 X 7 X 1mm (cell de-mounted), 145mm (cell mounted), 235mm with optional cell top lifting frame. Weight approx.: 5kg Issue 24/9/29 GDS Instruments Tel: +44 () Fax: +44 () e: [email protected] web:

2 HCA:2 Features The SS-HCA s (static) and SS-HCA d (dynamic) are both designed around the same central core of components. All of these components have been designed to give the machine high levels of axial and torsional stiffness coupled with the minimum amount of backlash and friction. All of these design considerations result in both machines being well suited for small strain testing right through to high load and strain testing. Both systems can be provided with the same optional sample sizes, transducers and celltop counter balanced lift. The SS-HCA s and SS-HCA d are both fully supported by and integrated into GDSLAB Control and Acquisition software SS-HCA s (Static version) The static version of the SS-HCA uses two high quality stepping motors controlled by a GDS-DPC motherboard. Axial displacements, axial loads, rotation and torque are applied through the same mechanical system as for the SS-HCA d. For the SS-HCA s, data acquisition uses the GDS Serial Pad. This provides 8 channels of 16 bit user definable data acquisition. Up to 7 additional data acquisition pads can be configured to the system for a total of 64 channels. The SS-HCA s provides a low cost HCA testing testing system without compromising the quality of the equipment. The SS- HCA s is particularly suited to very small strain testing in axial stress, axial strain, rotation or torque controlled tests. GDSLAB control software The GDSLAB control and acquisition software is a highly developed, yet extremely flexible software platform. Starting with the Kernel module and the ability to perform data acquisition only, additional modules may be chosen for your testing requirements. Some currently available modules are as follows: SATCON (saturation and consolidation) standard triaxial stress path testing (p, q and s, t) advanced loading tests unsaturated testing K consolidation Permeability Hollow Cylinder (static and dynamic) GDSLAB has the ability to be configured to your hardware of choice, no matter how unique the arrangement. A text file (*.ini) or initialisation file is created that describes the hardware connectivity to the PC. The hardware layout is available in graphical format via the GDSLAB object display. This makes setting up the devices and checking the connectivity extremely simple (see Fig. 1). Fig. 1 Object display showing a GDS SS-HCA arrangement For further information on GDSLAB, please refer to the dedicated GDSLAB datasheet. GDSLAB static HCA test module Independent control of the 5 principal parameters, i.e. Axial, rotational, outer cell pressure, inner cell pressure and back pressure. Axial Control by: Axial Stress (kpa), Axial Displacement, Axial Load (kn) Rotational Control by: Rotational Stress (kpa), Rotational Load (Nm), Rotational Displacement (degs) A phase shift offset angle may be introduced between axial and rotational axes when slow speed cyclic tests are being performed (see Fig. 2) Fig. 2 HCA static test setup module Issue 24/9/29 GDS Instruments Tel: +44 () Fax: +44 () e: [email protected] web:

3 HCA:3 SS-HCA d (Dynamic version) The heart of our dynamic SS-HCA system is a 16 bit Digital Control System (DCS). The DCS controls and measures torque, angular rotation, axial force and axial displacement, and is connected to the PC via a high speed USB connection. The data acquisition and control system resides external to the computer in order to give a realtime environment for control away from interference by the computer operating systems. The DCS gives direct closed loop servo control of axial force and displacement as well as torque and angular rotation. The SS-HCA d has two servo motors, one controlling axial movement and one controlling torsional movement. Axial force and deformation are applied through an actuator in the base of the cell. The torque is applied by the rotation of the same ram imposing the vertical force. Axial force and torque are measured by an internal submersible combined load and torque transducer. Axial displacement and rotation are measured using high resolution encoders read by the DCS. For dynamic testing, to further reduce backlash on the torque motor as the rotational load passes from positive to negative torque, an additional encoder for rotational feedback is installed. This second rotational encoder is positioned directly on the main ram which is used as the primary feedback control for the main motor, ensuring the motor control and the read value for the rotation is measured as close to the specimen rotation as possible. GDS DCS Digital Control System The GDS dynamic systems are all based around the GDS DCS high speed digital control system with closed loop feedback of displacement and load. With 16 bit data acquisition (A/D) and 16 bit control output (D/A), the GDS DCS runs at a control frequency of 1kHz per channel. This means that when running at 1Hz the system uses 1 control points per cycle. When running at 1Hz, it uses 1 control points per cycle The advantage of GDS DCS system is that no matter which dynamic system is purchased, they all use the same high speed control system. This ensures that the system has the highest level of functionality and reliability because all of our dynamic systems, over our complete range, use the same high specification control system. A result of this is that the accuracy and resolution of the test is only a function of the actuator used, whether it be a low cost pneumatic actuator, high accuracy electro-mechanical actuator or high capacity hydraulic actuator. GDSLAB dynamic HCA test module Dynamic cyclic loading tests at frequencies up to 5Hz (depending on the model). Provides sinusoidal cyclic control of axial displacement or axial force and rotational displacement/torque (see Fig. 3). A complete cycle of data can be saved every N cycles where the value of N is defined by the user. Controlled data displayed in real-time. Up to 1 points saved per cycle. Built in standard waveforms: Sinusoidal, triangular, square, havesine. User defined waveforms using 1 point ASCII file. Dynamic control of inner and/or outer cell pressure may be performed with the addition of optional dynamic pressure actuators. Fig. 3 GDSLAB test display showing dynamic cyclic test in progress Issue 24/9/29 GDS Instruments Tel: +44 () Fax: +44 () e: [email protected] web:

4 HCA:4 Pressure/volume controllers Pressure control for the outer and inner cell pressure and the back pressure are provided using GDS Digital pressure controllers. Example of hollow cylinder specimen after testing in a GDS SS-HCA The cell pressure and back pressure controllers may be mixed and matched.. There is the Standard Pressure/Volume Controller (STDDPC see Fig. 4), with pressure ranges from 1 to 4MPa, serial PC connectivity and 2 cc volumetric capacity. Fig. 4 The STDDPC Or there is the Advanced Pressure/Volume Controller (ADVDPC see Fig. 5) with pressure ranges of 2MPa, 3MPa or 4MPa with serial or IEEE PC connectivity and 2cc volumetric capacity. (Also, the ADVDPC 2MPa controller can be bought as 1cc volumetric capacity item required when using the larger sample sizes such as 4/2/16mm). Fig. 5 The ADVDPC The back pressure controller applies back pressure and also measures volume change of the test specimen, while the inner cell pressure controller measures volume change inside of the hollow specimen. Fig. 6 Hollow Cylinder Test Specimen Sample Preparation: The SS-HCA can be supplied with equipment for making toroidal samples in either cohesive (using the GDS soil Lathe, pictured in Fig. 7) or non-cohesive materials (using an internal, collapsible sample former). The manual soil lathe is suitable for all available sample sizes up to 4/2/16. The correct platens then need to be fixed to the lathe in order to prepare the required sample size. Platens for specific sample sizes are purchased separately to the lathe. Fig. 7 HCA soil lathe Why buy SS-HCA? Infinite rotation (i.e. >36 degrees possible) SS-HCA is a breakthrough in terms of price and performance. The precise control allows testing at very small axial and torsional strains. Software is supplied (GDSLAB) to fully control the HCA and can be programmed to control any stress or strain within the cell Flexibility in the capacity of the system (specimen size, load, pressures etc) ensures a system is created to specifically suit the testing required and the budget. Unsaturated testing may also be carried out using the SS-HCA (additional equipment may be required). May be used as a combined hollow cylinder/triaxial testing system. GDS worldwide technical support. Issue 24/9/29 GDS Instruments Tel: +44 () Fax: +44 () e: [email protected] web:

5 displacement axial load (kn) Double Amplitude World Leaders in Software Based Geotechnical Testing Systems for Laboratory and Field HCA:5 SS-HCA d, Example dynamic system performance for axial axis based on a 5Hz machine. Note: performance will vary for machines other than 5Hz kn +/-5kN 4 2 5kN +/-5kN Frequency (Hz) with 5kN force datum with zero kn force datum Frequency Amplitude Double amplitude Amplitude Double amplitude (Hz) Typical test results Axial displacement feedback control Frequency (Hz) 1. Peak to peak 2. Radial stress (kpa) time (seconds) displacement Due to continued development, specifications may change without notice. Issue 24/9/29 GDS Instruments Tel: +44 () Fax: +44 () e: [email protected] web: